Method for the production of catalytically active mixed phases

ABSTRACT

Method for the production of catalytically active mixed phases in powder form from precursors which contain the elements of the mixed phase and are treated thermally and mechanically. 
     The precursor or precursors contained in a solution or suspension are applied to heated surfaces of moving heat carrying bodies and precipitated and dissociated on them with evaporation of the solvent or of the liquid component of the suspension. The mixed phase formed on the heat carrying bodies is removed from the heat carrying bodies and then, to prepare it for further use, it is crushed.

The invention relates to a method for the production of catalyticallyactive mixed phases in powder form, from precursors which contain theelements of the mixed phases, with thermal and mechanical treatment.

Numerous methods are known for the preparation of catalytically activemixed phases of, for example, ternary or quaternary oxides as a basisfor the production of catalysts. The manufacturing methods depend on thestructure of the desired phase. Usually these manufacturing methods arebased on solid reactions in which individual oxides are mixed with oneanother and then subjected to a heat treatment. Other methods are basedon precipitation processes in which the mixed phase is precipitated froma suspension or solution of precursors. In these methods metal salts ororganometallic compounds are usually subjected to a precipitation,dried, and crushed, a cure is performed, then they are again dried,shaped and finally again subjected to a heat treatment. Such methods donot in all cases result in pure mixed phases, even when specialattention is given to the conduct of the method as regards thetemperatures and pressures to be used. In these cases binary oxides arebound into the desired mixed phase as impurities, so that, among otherthings, catalytic properties are substantially diminished. However, allthese previously known methods are based on a great number of processsteps entailing complex apparatus and correspondingly high installationcosts.

The invention is addressed to the problem of substantially simplifyingthe method for the production of catalytically active mixed phases inpowder form, and of preparing the desired mixed phases withoutimpurities, with less complex apparatus and lower installation cost,preferably at atmospheric pressure and at a lower temperature level.

Setting out from a method of the kind mentioned above, this problem issolved in accordance with the invention in that the precursor containedin a solution or suspension is brought onto heated surfaces of movingheat carrying bodies, and precipitated and dissociated or, morespecifically, decomposed on the latter by evaporating the solvent, themixed phase formed on the heat carrying bodies is removed, and the solidmixed phase is then crushed. On account of this method of procedure, aconstantly self-renewing, wettable heat carrying surface is to be madeavailable at a temperature level corresponding to the evaporationtemperatures of the suspension or solution, which enables the process tobe arranged in a continuous series of the individual stages.

In further development of the invention, the surface of the heatcarrying bodies is heated to a higher temperature level exceeding theevaporation temperature of their solvent. In this manner it becomespossible not only to precipitate and dissociate or decompose theprecursor, but at the same time to perform the calcination of the mixedphase, thus reducing the amount of time required for the production ofthe mixed phase in powder form.

The economy of the method for the production of catalytically activemixed phases can be further improved by continuously removing thevolatile component of the solvent or suspension, separating it from thisentrained solid matter, and feeding it to the portion of the mixed phasethat is directly withdrawn from the process.

In a preferred development of the invention, within a reactor whosecircumference is circular in cross section or in the shape of a polygonapproaching a circle, the mixed phase is removed from the surfaces ofthe heat carrying bodies by the relative movement within the bed of thebodies, and furthermore the mixed phase is simultaneously ground as wellas separated continuously or discontinuously from the circuit of theheat carrying bodies. By this procedure the individual steps of theprocess are performed within a moving bed of the heat carrying bodies,and the temperature of the bodies can be adapted to the optimum for theindividual steps of the process. It is thus possible to avoid exceedingor falling below the temperature level which would result in losses inthe activity of the mixed crystals that are formed.

The way in which the heat carrying bodies are circulated is furthermorepracticed advantageously within a reactor disposed for rotation about anapproximately horizontal axis and having a spherical circumference or apolyhedral surface approaching the spherical shape, the heat carryingbodies being advanced continually upward by contact with the reactorwall, falling back down by gravity, and being turned over.

Especially advantageous toward maintaining the temperature within closetolerances is a method in which the heat carrying bodies, in a reactorwith a tubular outer wall and an axis of rotation inclined from thehorizontal are transported upward by contact with the reactor wall inthe direction of rotation of the reactor, and fall down again bygravity, and at the same time are carried axially as well as turnedover, from the point where the precursor enters to the point where themixed phase is removed at the other end of the tubular reactor, andfurthermore the heat carrying bodies are positively returned, after theremoval of at least a portion of the mixed phase, to the area where theprecursor is fed in. The term, "tubular reactor," is also to beunderstood to refer to a reactor of a substantially conical ortruncoconical configuration.

In a configuration different from this the heat carrying bodies arecarried substantially by gravity vertically downward and at the sametime turned over within a reactor with a substantially vertical axis ofsymmetry by relative movement of the reactor wall, from an upper pointof entry of the precursor to a lower exit of the heat carrying bodies,and furthermore the heat carrying bodies are positively returnedvertically upward from their point of exit to the point of entry of theprecursor, completing their circuit. In this variant, with a verticalarrangement of the vessel axis above the point of entry of theprecursors and [the point] of the formation of the mixed phase, a quasistatic bed of the heat carrying bodies can be disposed as a filterand/or an additional one can be disposed in order to limit emissions.

The reheating of the heat carrying bodies, or the adjustment of theirsurface to the temperature level necessary for the individual section ofthe process, can be performed advantageously especially by deliveringheat to them, during their movement within the reactor, indirectlythrough the reactor wall and/or through the means used to propel them.The ball diameter or the ratio of mixture of balls of different diameteris in this case made dependent upon the desired fineness of grind an theoptimum temperature for the precipitation and dissociation decompositionor simultaneous calcination thereof. By the vertical stratification ofballs of different diameter that develops, the grinding function isbetter separated from the heat carrying function.

BRIEF DESCRIPTION OF THE DRAWING

To explain the method of the invention, FIG. 1B will be compared in theaccompanying drawing with a precipitation method of FIG. 1A inaccordance with the state of the art.

In the block diagram A there is shown a precipitation process inaccordance with the state of the art, taken from "Catalyse de Contact,"le Page, Inst. Francaise du Petrole, p. 396.

The precursors 1 and 2 are in this case fed to a stirring container inwhich the precipitation is performed. Then the precipitate obtained issubjected to a preliminary dewatering and then to a secondary drying.The dry substance obtained in this manner is then crushed and afterwardsubjected to a curing process in another process apparatus. Moisture isagain removed in dryers from the product obtained by this curingprocess, prior to the calcination of the previously obtained drysubstance in kilns.

The individual steps of the procedure in accordance with the inventionare to be seen in diagram B.

Starting with the placement of the precursors on the surfaces of movingheat carrying bodies, the precursors are concentrated on them byevaporation, and decomposed, and then the mixed phase is calcined. Thecatalytically active mixed phase that is formed is then removed from thesurfaces of the heat carrying bodies and ground, and dischargedcontinuously or discontinuously, in accordance with the desired finenessof grind. Through the free choice of the process parameters, especiallythe temperature management within the moving bed, the length of time forwhich the bodies are stirred, and their relative velocity, it ispossible to form optimum liquid film thicknesses as well asprecipitations on the heat carrying bodies within optimum rates ofprecipitation, which equally determine the nucleation and seed growthrate of the solid phase. The same applies to the temperatures in thecalcination and the fineness of grind.

EXAMPLES

A drum with a diameter of 350 mm and a depth or length of 300 mm, waspacked with commercial corundum grinding balls in the amount of 10 kg,and a ball diameter of 8-15 mm. The drum was slightly tilted from thehorizontal and mounted for rotation by a motor through a controllabletransmission. The precursor was fed onto the ball packing at theelevated end of the drum through a lance within a bore disposed axiallyin the center in the end wall of the drum and the mixed phase wasdischarged in powder form at the opposite end. For the discharge of themixed phase the lower end had an annular gap between the wall of thedrum and a central disk. The rotational speed of the drum was 4 to 6revolutions per minute. The outer wall of the drum was heated by gassurface burners connected in series over the depth of the drum. Thesurface temperature of the grinding balls was kept constant at 450° C.,the temperature fluctuations amounting to no more than ±50° C. Thetemperature control was performed by varying the throughput of theprecursor.

Example 1

For the production of copper manganate (CuMn₂ O₄), a precursor solutionof molar copper nitrate solution and bimolar manganate nitrate solutionwas fed into the drum. A powder was obtained which, on the basis ofX-ray structural analysis in accordance with ASTM 11-480, corresponds tothe CuMn₂ O₄ phase.

In the usual manner, the glancing angle obtained by the X-ray analysiswas compared with the ASTM standards.

Example 2

A powder was obtained which corresponds to the phase CuCr₂ O4 accordingto X-ray structural analysis per ASTM 26-508.

As previously described, the glancing angles obtained on the basis ofthe X-ray structural analysis were compared with the ASTM standards.

Example 3

For the production of a mixed phase of titanium-vanadium oxide, aprecursor hydrolyzate of titanium tetrachloride in water was preparedwith ammonium vanadate dissolved in it. By spraying this precursor in aspray dryer at 350° C. and then calcining it at 450° C. for one hour, anochre-yellow to brown colored powder is obtained. The brownish yellowcolor points to a content of free vanadium pentoxide in the mixed phase.After dissolving the free vanadium pentoxide out of the mixed phase with0.5-molar oxalic acid, a dark green to anthracite-colored powder isobtained. The amount of vanadium oxide dissolved out can be determinedby photometry in the separated solution.

Example 4

For the preparation of a mixed phase of titanium-vanadium oxide, aprecursor hydrolyzate of titanium tetrachloride in water was preparedwith ammonium vanadate dissolved in it as in Example 3.

By spraying the precursor onto a heated drum whose temperature was 450°C., a powder was obtained whose yellow-brown, slightly greenish colorpoints to a content of free vanadium pentoxide in the mixed phase, in amanner similar to Example 3. The free vanadium oxide was again dissolvedout of the mixed phase with 0.5-molar oxalic acid. After filtration adark green to anthracite-colored powder is again obtained. In theseparated solution the amount of vanadium pentoxide dissolved out can bedetermined by photometry.

Example 5

For the production of a mixed phase of titanium-vanadium oxide, aprecursor hydrolyzate of titanium tetrachloride in water was preparedwith ammonium vanadate dissolved in it, and then, in accordance with themethod of the invention, it was placed on a charge of balls within adrum the same as in the procedure described in Examples 1 and 2. A darkgreen to anthracite-colored powder was obtained, which has a BET surfacearea (surface area measurement according to Brunauer/Emmett and Teller)of 90 m² /g. The color of the mixed phase obtained indicates anegligibly small content of the undesired component free vanadiumpentoxide in the mixed phase. Thus the ratio of titanium and vanadium inthe mixed phase corresponds to the ratio in the precursor. For thespecial application, this ratio can thus be adjusted directly bychoosing the corresponding solution. The small content of free vanadiumpentoxide in the mixed phase can be determined as described in Examples1 and 2.

In a test apparatus, 1 g of the powder obtained in accordance withExamples 3-5 was weighed in and flooded with a gas mixture of 1000 ppmNO, 1000 ppm NH₃, 3% oxygen, balance N₂. The rate of flow of the gasmixture at 25° C. was 13.5 cm³ /sec. The rate of the reduction of NO wasdetermined in relation to the reactor temperature.

                  TABLE 1                                                         ______________________________________                                        Sample per                                                                    Example No.                                                                            200° C.                                                                         250° C.                                                                         300° C.                                                                       350° C.                                                                       400° C.                       ______________________________________                                        3        50       77       86     62      0                                   4        63       88       97     99     95                                   5        86       99       100    100    100                                  ______________________________________                                    

For the mixed phase, a titanium to vanadium atom ratio Ti:V=1:0.18 wasestablished in the precursor in all examples.

The above table indicates a considerable loss of activity in thehigh-temperature range in the mixed phases prepared by the conventionalmethods in Examples 3 and 4. This activity loss is connected with thepresence of free V₂ O₅.

In the following table the extinctions of the solutions in Examples 3 to5 are shown, which were obtained by dissolving the free vanadiumpentoxide on 0.5-molar oxalic acid.

                  TABLE 2                                                         ______________________________________                                        Sample in accord with Example                                                                    3        4       5                                         Extinction at 780 mm                                                                             0.851    0.73    0.125                                     ______________________________________                                    

The extinction characterizing the vanadium pentoxide in the solution andthus the free vanadium pentoxide in the mixed phase correlates with theactivity loss at high temperatures as indicated in Table 1.

By the method in accordance with the invention numerous other mixedphases can be produced advantageously, in virtually pure form, withother systems of substances. Examples of such mixed phases are ironmolybdate mixed phases or bismuth-nickel-iron molybdate mixed phases.

The powder obtained is applied to support structures in the usual manneras the catalytically active compound. For this purpose commercialbinding agents are used, preferably those used for ceramic compositions.The method of the invention furthermore offers the possibility ofselecting the grain size distribution of the solid mixed phase productby varying the rotatory speed, the ball size and the degree of fill inthe reactor.

We claim:
 1. Method for the production of catalytically active mixedphases in powder form from precursors which contain the elements of themixed phases, with thermal and mechanical treatment, in which method theprecursor contained in a solution containing a solvent is applied toheated surfaces of moving heat carrying bodies, precipitated on saidbodies with evaporation of the solvent, and decomposed, and calcined,the mixed phase formed on the heat carrying bodies is removed from theheat carrying bodies, and the mixed phase is subsequently crushed. 2.Method in accordance with claim 1, wherein the precursor is precipitatedon surfaces heated above the evaporation temperature of its solvent andat the same time decomposed as well as calcined.
 3. Method in accordancewith claim 1 or 2, wherein the volatile component of the solvent iscontinuously removed, the solid matter carried with the latter isseparated, and is delivered to the portion of the mixed phase that iswithdrawn directly from the process.
 4. Method in accordance with claim1 or 2, wherein, from the surfaces of the heat carrying bodies within areactor having a wall configured in cross section as a circle or as apolygon approaching a circle, the mixed phase is continuously removed byits relative movement within its bed, and furthermore the mixed phase issimultaneously ground as well as continuously or discontinuouslyseparated from the circuit of the heat carrying bodies.
 5. Method inaccordance with claim 4, wherein the heat carrying bodies, within areactor disposed for rotation about an approximately horizontal axis andhaving a spherical circumference or a polyhedral surface approaching aspherical one, are continuously driven upwardly by contact with thereactor wall and carried downward as well as turned by the force ofgravity.
 6. Method in accordance with claim 4, wherein the heat carryingbodies, within a reactor with a tubular periphery and with an axis ofrotation disposed at an inclination from the horizontal, are drivenupward as well as turned over by contact with the reactor wall in itsdirection of rotation and downward by the force of gravity and at thesame time they are driven axially from the entry of the precursor at theone end to the discharge of the mixed phase at the other end of thetubular reactor.
 7. Method in accordance with claim 6, wherein the heatcarrying bodies are taken out at the lower end of the reactor and, afterremoval of at least a portion of the mixed phase, they are positivelyreturned to the area of the entry of the precursor.
 8. Method inaccordance with claim 4, wherein the heat carrying bodies are carried bythe force of gravity, and simultaneously stirred, automatically downwardvertically within a reactor with a substantially vertical axis ofsymmetry, with relative movement of the reactor wall, from an upperentry of the precursor to a lower discharge of the heat carrying bodies,and furthermore the heat carrying bodies are subsequently returnedpositively vertically upward from their discharge into the area wherethe precursor enters.
 9. Method in accordance with claim 4, wherein heatis indirectly fed through the wall of the reactor to the heat carryingbodies during their movement within the reactor.
 10. Method inaccordance with claim 8, wherein heat is indirectly fed to the heatcarrying bodies through means which are used to propel said bodies.